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Subject[PATCH] seq_file:update file->f_pos when lseek() to m->read_pos
Date
After pread(), file->f_pos and m->read_pos get different,
and lseek() to m->read_pos did not update file->f_pos, then
a subsequent read may read from a wrong position, the following
program shows the problem:

char str1[32] = { 0 };
char str2[32] = { 0 };
int poffset = 10;
int count = 20;

/*open any seq file*/
int fd = open("/proc/modules", O_RDONLY);

pread(fd, str1, count, poffset);
printf("pread:%s\n", str1);

/*seek to where m->read_pos is*/
lseek(fd, poffset+count, SEEK_SET);

/*supposed to read from poffset+count, but this read from position 0*/
read(fd, str2, count);
printf("read:%s\n", str2);

Signed-off-by: Jiaxing Wang <hello.wjx@gmail.com>
---
fs/seq_file.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 774c1eb..4b22b26 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -328,7 +328,8 @@ loff_t seq_lseek(struct file *file, loff_t offset, int whence)
m->read_pos = offset;
retval = file->f_pos = offset;
}
- }
+ } else
+ file->f_pos = offset;
}
file->f_version = m->version;
mutex_unlock(&m->lock);
--
1.8.1.2


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